This article was originally published in the July/August 1999 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.

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Home Energy Magazine Online July/August 1999

trends

in energy

Cutting-Edge Blades Slash Fan Energy Use

The Gossamer Albatross features a specially designed propeller with a true airfoil.

The Gossamer Wind prototype fan features blades that follow the design of the propeller; they move air more efficiently.

Figure 1. Measured performance of the fans at high speed. Only the Emerson CF4852 was able to match the air flow performance of the 52-inch Gossamer Wind prototype, and only at a considerable energy cost.

Ceiling fans can be an efficient way to cool people down in moderately warm weather. However, while they do create a breeze on the body and lower skin temperature, their motors use electricity inefficiently and also generate heat. Despite this, ceiling fans are here to stay--the vast majority of homes have them. That's why there's a big need for more efficient ceiling fans that use less energy and thus create less heat.

Researchers at the Florida Solar Energy Center (FSEC) are aiming to meet that need. They have developed a ceiling fan with efficient blades that are modeled on the same technology that allowed a human-powered plane to fly across the English Channel. This fan can save up to 50% in energy use over conventional ceiling fans. Called the Gossamer Wind fan, it is set to hit the market in September.

Teamwork for New Technology
The Gossamer Wind fan got its start in the fall of 1996, when FSEC researchers set out to improve three areas of current ceiling fan design: the blades, the controls, and the motor. FSEC wanted to see if a fan with better blades and a smaller motor could perform as well as the best currently available ceiling fans--and also be more energy efficient. The researchers wanted to achieve the maximum air flow (in CFM) per input watt, while providing uniform air flow distribution throughout the room and quiet operation.

For improving the fan blades, FSEC approached AeroVironment Incorporated of Monrovia, California, inventors of the Gossamer Albatross airplane. Based on their expertise in propeller blade design, AeroVironment designed new blades with a true airfoil. The blades are tapered, with the outer portion being narrower than the inner one. The taper provides even loading (lift and thrust) across the width of the blade, so that the fan is less prone to wobble. The blades provide roughly twice as much air-moving efficiency as conventional flat blades. The design was optimized for fans that run at 200 rpm.

FSEC put together two prototypes of the fan, one with a 52-inch diameter, and another with a 64-inch diameter. Researchers tested these prototypes against three leading flat-bladed fans. FSEC originally wanted to use a smaller, more efficient motor, but because high-efficiency motors are not readily available for commercial production, they gave the Gossamer Wind fan a standard 50W fan motor with an efficiency of about 3% on low speed and 13% on high. (The low efficiency comes from the fact that shaded-pole motors are very inefficient.) The Gossamer fans also have a smaller motor than most flat-bladed fans, so they use less electricity and generate less heat.

Passing the Test
FSEC tested the Gossamer Wind prototypes against three flat-bladed fans: the Emerson CF705, the Emerson CF 4852, and the Hunter Summer Breeze. The fans were tested in terms of air flow (m/sec), power (W), and speed (rpm). The performance of the 52-inch Gossamer Wind prototype is clearly superior to that of the flat-bladed fans (see Figure 1).

Because the Emerson CF705 and the 52-inch Gossamer Wind prototype have the same size motor, the fact that the Gossamer outperformed the Emerson was due solely to the efficiency of its propeller blades. The air-moving efficiency of this motor was increased by 86% at low speed--nearly doubling its overall performance.

The low-speed performance of the Hunter fan approaches that of the Gossamer Wind prototype (see Table 1) because the Hunter's highly pitched blades produce air flow that is highest toward the edge of the blade tips, which encompasses a larger area.

At high speed, the Gossamer Wind prototype showed an increase in air-moving efficiency of 110% relative to the Emerson CF705. It also had the greatest total air flow--even more than the Emerson CF4852, with a motor drawing 88% more power (see Table 2).

Buoyed by the success of these tests, AeroVironment and FSEC soon began looking for a manufacturer. Catalina Lighting Industries of Miami, Florida, agreed to manufacture the fans and began negotiations with Home Depot to carry them in its stores nationwide. They will be the most energy-efficient fans on the market. The basic model will sell for roughly $60 to $70, about the same as other, similar ceiling fans. More advanced models with special features will sell for as much as $200.

Special Features
Advanced models of the Gossamer Wind fan will have several different special features. One is an energy-efficient light kit that can provide up to 12,000 hours of superior lighting without a lamp change. FSEC adapted a 20W Circline fluorescent lamp (Lights of America: 2620C-MPF) to fit within the standard lens of the light kit housing. Six J-type, 100W R7S incandescent lamps would have to be replaced over the same time period. This light kit can reduce associated energy use by 80%, saving approximately $10 per year and reducing the frequency with which bulbs must be changed by 83%.

Another special feature is the 360° infrared motion sensor control, which automatically activates the fan when anyone enters a room and turns it off when occupants are gone. The control is sensitive to time as well as motion, and also has an override switch.

One feature that consumers sometimes look for in fans is a reverse switch that allows air to be pulled up; this feature is not available in the Gossamer Wind fan. Patents for both the ceiling fan blade and the automatic control system are pending.